1. Field of the Invention
This invention relates generally to an optical computing method or process and to devices and systems for practicing such method. More particularly, this invention relates to optical methods and arrangements for converting optical intensity to position mapping for performing digital logic functions.
2. Description of the Prior Art
Reference may be had to "Optical Logic and Optically Accessed Digital Storage" by Rolf Landauer in Optical Information Processing, Y. E. Nesterikhin et al., ed., Plenum Press, 1976, pp. 219-253, for some general background with respect to optical arrangements for performing logic functions.
Fiber and integrated optics logic are treated by H. F. Taylor, "Guided Wave Electro-Optic Devices for Logic and Computation", Applied Optics, 17, pp. 1493-1498 (May 15, 1978), and by Lew Goldberg and Sing H. Lee, "Integrated Optical Half-Adder Circuit", Applied Optics, 18, pp. 2045-2051 (June 15, 1979). Unlike the present invention, these systems do not embody parallel processing, they are hard-wired, and are not readily reprogrammed.
David H. Schaefer and James P. Strong, III, in a paper entitled "Tse Computers", proceedings of IEEE, 65, pp. 129-138 (January 1977), describe an arrangement consisting of an array of optical detectors and sources coupled by electronic logic circuits. These arrays are coupled by optical fibers. There are severe difficulties manufacturing the circuit arrays.
Ravindra A. Athale and Sing H. Lee, in a paper entitled "Development of an Optical Parallel Logic Device and a Half-Adder Circuit for Digital Optical Processing", Optical Engineering, 18, pp. 513-517 (1979), describe a liquid crystal device and demonstrate an 8.times.8 AND gate using parallel logic and control provided by a photoconductor matrix. The approach discussed here as well as that of the Tse computer share the limitations of integrated optics in that presently only simple gates can be implemented directly and the functions cannot be programmed.
Kendall Preston, Jr., in Chapter 8 of Coherent Optical Computers, McGraw-Hill, New York, 1972, and C. C. Guest and T. K. Gaylord, in a paper entitled "Two Proposed Holographic Numerical Optical Processors", SPIE Proceedings on Optical Processing Systems, Vol. 185, pp. 42-49, have proposed holographic optical processing schemes. In these, extreme alignment accuracy and stability are required.
All of the above systems (excepting Tse) have a level restoring problem. One beam propagates through the entire system. Noise and attenuation accumulate. In such arrangements repeaters may offer a solution to such system problems but these are difficult to fabricate and only further complicate the system.
In accordance with presently preferred embodiments of this invention, a variable grating mode liquid crystal device is utilized to provide optical intensity to position mapping. Such devices may operate in a transmissive mode or in a reflective mode for readout purposes depending upon their construction. Although the variable grating mode liquid crystal device is not discussed therein, reference may be had to U.S. Pat. No. 3,824,002 to Terry Beard, assigned to Hughes Aircraft Company, for general information on the construction and operation of a liquid crystal light valve which operates in the reflective mode. In a reflective mode device, the optical input is applied to one side of the liquid crystal light valve and the readout light beam is applied to the other side. In a liquid crystal device which operates in the transmissive mode, both of the writing and the readout beams are applied to the same side of the liquid crystal device.